1. Field of the Invention
The present invention relates to measuring runout and, more particularly, to measuring runout of aircraft gas turbine engine fan shrouds.
2. Description of Related Art
High by-pass aircraft gas turbine engines include a large fan section with large fan blades that seal radially outwardly against an abradable shroud disposed within a fan casing of the engine. Clearance between aircraft engine fan blade tip and the shroud has a direct impact on engine fuel burn performance and, in some cases, engine integrity. As such, accurate measurement of the fan blade clearance is important.
Part of this measurement requires accurate measurement of the fan shroud runout. Runout is a function of the distance between an engine centerline about which a rotor, including the fan, of the engine rotates and the shroud as a function of angular position around the shroud. There is a great need for a fast, accurate and precise method for measuring fan shroud runout for the full circumference or to automatically track runout angle in conjunction with the runout magnitude. Present methods include fixing an attachment to stationary engine structure to measure runout angle and measurements are done using dial gauges in stages at intervals around the fan shroud requiring fixing and refixing the attachment.
Fan shroud runout measured using a dial indicator and visually approximating the angular location is a tedious operation and the runout is only recorded at a few discreet locations and is manually recorded. This current technique lends itself to many sources of error including positioning error and limiting the number of measurement to only a few locations. This method only provides an approximation of the actual case runout and the maximum runout condition can be missed if the maximum runout value is not at one the measured locations. Better angular positioning can be obtained with a rotary encoder, but these devices require and attachment to the stationary structure and this is not practical due to the size of the tooling involved. This measurement technique used for every production engine is time consuming and is not desirable in a production or overhaul environment. The results generated by the current method are only an approximation of the fan shroud runout due to the limited number of data points gathered. In addition, this current measurement technique for the large engines such as the General Electric GE90 engine requires that one fan blade not be installed in order to install the measurement tooling. This interruption of the assembly flow also adds cycle time and cost to the overall process.
It is highly desirable to improve accuracy and speed of and to automate the measurement, recording, and analysis of fan shroud runout.